sign in sign up
<<
Home , Microbial loop

Palmer LTER:

J G O F S • LT E R C E A N T I M Microbial Processes in an Ice-Dominated Marine I O E - S A I E R AW I E H O S • • T 0° H 158°W PALMER 22°45'N STATION STATION M. Church, C. Carrillo, K. Bjorkman, S. Kerr, J. Christian, M. Karner, L. Tupas, ALOHA

& 90° 90° C W E S O C U I D. Bird, E. DeLong, S. Donachie, and D. M. Karl P C 180° M L D E • • A D O • L N O D Y C E & A N - G E S U I C E L I N K A Department of Oceanography, University of Hawaii, Honolulu, HI. 96822 N I A I I V E R S I T Y o f H AW DISCOVERY OF We now recognize three domains of life: Archaea, and Eucarya ABSTRACT (right). Until recently, planktonic Archaea were not even recognized as a As one component of a -based study of shelf and slope waters west of the potential component of the marine microbial loop. That all changed in MAJOR RESEARCH FOCI 1992 when DeLong and colleagues discovered a high of • Carbon-oxygen inventories and fluxes Antarctic Peninsula, our project is focused on inorganic and organic carbon inventories and fluxes, especially the role of heterotrophic (Bacteria and Archaea). Our Archaea in Antarctic coastal marine . Since that time we • Microbial structure and function experimental approach is designed to describe the coupling between photoautotrophic carbon have collected Archaea (both marine group I and II) abundance data in • Comparative ecosystem analyses production and heterotrophic carbon utilization by measuring various components of the both austral summer and winter, and within each season have sampled numerous surface and deep water masses. Our ongoing investigations Paired epifluorescence micrographs of a 1000-m deep water sample showing (left) microbial loop, including standing stocks, production rates, as well as predator and Archaea group-I positive cells and (right) total DAPI-stained cells. KEY MICROBIAL PARAMETERS AND PROCESSES: controls on . This research program is located in a climate-sensitive region indicate that Archaea can dominate at certain times (see below). Their THE MICROBIAL LOOP MATERIALS AND METHODS influenced by the extent and duration of sea-ice. Significant results document a temporal ecological role is not known at present, but they presumably share Schematic representation of the oceanic showing, on left, the • Community structure uncoupling of auto- and heterotrophic processes, the presence of relatively high percentages of metabolic resources with the heterotrophic bacteria. classical pathway of carbon and through the photosynthetic - epifluorescence microscopy planktonic Archaea, especially in deep (>100 m) water, and significant seasonal and interannual Eucarya, to and on to the higher trophic levels. Depicted on - fluorescent in situ hybridization with rRNA variability in microbial dynamics. Comparative ecosystem analyses with similar data sets from the right is the present view of the , which utilizes targeted polynucleotide probes () ongoing research in the N. Pacific gyre reveal insights into microbial strategies for survival in the energy stored in the large detrital carbon pool to produce microbial • Standing stocks global ocean. that can re-enter the biogenic . Cell-associated - lipopolysaccharide (LPS) concentration ectoenzymes (Ecto) enable Bacteria to utilize high molecular weight - dual-laser flow cytometry WHY ANTARCTICA? (HMW)-DOC. Also shown in the microbial web are viruses and the - microbial biomass "closure" calculations • Cold waters dominate our planet but microbial processes Archaea. At the present time we have only a rudimentary knowledge of (POC, ATP, LPS) are poorly understood – Antarctica is a "natural laboratory" the role of Archaea in the oceanic food web. Shown at the bottom of this • Production rates Carbon fluxes are globally significant diagram is the downward flux of particulate carbon (and energy) which - carbon/energy flux • is now thought to fuel most subeuphotic zone processes. Microbial loop - transition zone is strong CO2 sink - ectoenzyme activities - export production is high but erratic structure and function are the central research foci of the Pal-LTER - organic perturbation experiments - large repository of unused surface nutrients and Carbon Flux team. - temperature perturbation experiments - O2 dynamics and fluxes • Susceptible to global environmental change - ice dynamics • Population controls - deep water ventilation and bottom water formation - dilution grazing experiments - ozone hole and UV flux - viral lysis - DOM availability CONCLUSIONS - variability POPULATION DYNAMICS The proximate controls on the abundance and of heterotrophic bacteria • We have observed a dramatic uncoupling of bacterial and algal processes are presumed to be either top-down (grazing), bottom-up (resource) or, perhaps, • Microbial loop processes appear to be negligible relative to the magnitude BACTERIAL-ALGAL RELATIONSHIPS of -dominated carbon fluxes Bacterial carbon and carbon are typically highly temperature (i.e. growth rate control). Although much of the dissolved organic matter correlated in aquatic . This derives from our current in the sea is uncharacterized and therefore of unknown bioavailability, we have not • The combined effect of organic substrate availability, grazing and understanding of the microbial loop: phytoplankton produce organic observed the predicted increase in either DOC or DON with increased phytoplankton temperature appears to be the most likely explanation for our field matter that is utilized by bacteria. Several empirical relationships (see A biomass, as measured by chlorophyll (see C and D below). Consequently, it is possible observations below) have been published including Bird and Kalff (1984) and Cole et al. that bacteria in the Pal-LTER region are resource-limited. • Previously undescribed planktonic Archaea are an important component (1988). However, in Southern Ocean ecosystems there appears to be a of the Southern Ocean microbial loop and, at times, they outnumber decoupling of carbon production and carbon utilization processes and a An interesting cross-ecosystem observation from measurements of the activities of two Bacteria deficit of bacteria, by up to an order of magnitude, relative to aquatic key ectoenzymes in heterotrophic metabolism (leucine aminopeptidase [LAPase] and • Heterotrophic microbial processes in the Southern Ocean may be in temperate and tropical regions. Furthermore, bacterial beta-glucosidase [BGase]) reveal fundamental differences among microbial significantly affected by global environmental change production in the Pal-LTER region is typically less than 5% of the assemblages sampled from different regions and, in the case of Southern Ocean contemporaneous (see B below) compared to 20- microbes, large variations in the BGase/LAPase ratio depending on time of year. On 30% in temperate regions, and is not well correlated with total primary average it appears that bacteria from Antarctic waters sustain relatively high LAPase SELECTED REFERENCES production. activity levels and relatively low BGase activity levels which probably are a reflection of KARL, D. M. 1993. Microbial Processes in the Southern Ocean. In E. I. Friedmann, resource availability. Compared to their equatorial counterparts, bacteria in the Pal- ed., Antarctic Microbiology, pp. 1-63. John Wiley and Sons, Inc. HYPOTHESES FOR LTER study area are "meat-eaters" (see E below). NOT EVEN THE TIP OF THE ICEBERG! SOUTHERN OCEAN UNCOUPLING DELONG, E. F., K. Y. WU, B. B. PRÉZELIN and R. V. M. JOVINE. 1994. High OF ALGAL-BACTERIAL PROCESSES Grazing by heterotrophic nanoflagellates (HNF) may ultimately control bacterial Knowns abundance of Archaea in Antarctic marine picoplankton. Nature 371: 695-697. population dynamics. In the Pal-LTER study area, HNF abundance falls both lower • Less than 1% of species in culture • Differential temperature effects and higher than observed values from the literature when scaled to bacterial • Only 1 "model" system (E. coli) GASOL, J. M. 1994. A framework for the assessment of top-down vs bottom-up • Bacterial substrate limitation abundance (see F below). For some portions of the LTER region, the HNF abundance Unknowns control of heterotrophic nanoflagellate abundance. Marine Progress Series 113: Chemical antagonism equals or exceeds the theoretical "maximum attainable biomass" (solid line) based on 291-300. • resources as derived from the model of Gasol (1994). This is rarely observed in • Novel microbes and habitats • Direct between bacteria and temperate habitats, and suggests that grazing may play a very important role in south • Novel physiology/ biochemistry/ecology CHRISTIAN, J. R. and D. M. KARL. 1995. Bacterial ectoenzymes in marine waters: HABITAT VARIABILITY algae for organic compounds polar habitats. activity ratios and temperature response in three oceanographic provinces. Southern Ocean ecosystems are heterogeneous, exhibiting the greatest and Oceanography 40: 1042-1049. seasonal variability on Earth. This is especially true for the Pal-LTER 1000 region which hosts a large interannual variability in sea ice duration and 100 4 KARL, D. M., J. R. CHRISTIAN, J. E. DORE and R. M. LETELIER. 1996. extent. These factors directly influence the nature, timing and intensity Microbiological oceanography in the region west of the Antarctic Peninsula: Microbial of various microbial loop processes. For example, in the Pal-LTER study ) 3 dynamics, nitrogen cycle and carbon flux. In R. M. Ross, E. E. Hofmann and L. B. area particulate ATP concentrations (a measure of total microbial -1 Quetin (eds.), Foundations for ecological research west of the Antarctic Peninsula. biomass) vary nearly 3 orders of magnitude between austral winter 100 2 Antarctic Research Series, vol. 70. American Geophysical Union, Washington, D.C., (July) and austral summer (Jan). The wintertime values are the lowest g C l µ pp. 303-332. ever measured for surface ocean waters, and the summertime maxima M)

µ 1 are among the highest values ever recorded for non-polluted waters. CARRILLO, C. J. and D. M. KARL. 1999. Dissolved inorganic carbon pool dynamics

50 (BGase) These extreme annual variations suggest that microbial growth rate in Northern Gerlache Strait, Antarctica. Journal of Geophysical Research 104: 15,873- selection, carbon/energy flow optimization and community succession 10 0 10 DOC ( 15,884.

may be very important criteria in the structure and function of Southern Log Bacterial C ( Ocean food webs. -1 MURRAY, A. E., K. Y. WU, C. L. MOYER, D. M. KARL and E. F. DeLONG. 1999. Evidence for circumpolar distribution of planktonic Archaea in the Southern Ocean. Particulate ATP (ng l-1) A -2 Aquatic 18: 263-273. C E 0 1000 0 10 20 30 1 1 10 100 1000 10000 -3 BIRD, D. F. and D. M. KARL. 1999. Uncoupling of bacteria and phytoplankton during 0 -1 0 PhytoC (µg C l ) 0 10 20 30 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 the austral spring bloom in Gerlache Strait, Antarctic Peninsula. Aquatic Microbial -1 1000 Chl a (µg l ) log10 (LAPase) Ecology 19: 13-27.

10 5 10 ) 50 , 0-20 m) -1 -1 d -2 4 100 10

100 M) µ 3 Depth (m) 5 10 DON ( 10

150 2 10 B D F Heterotrophic nanoflagellates (ml 200 Bacterial production (mg C m 1 0 10 0 10 20 30 5 6 7 8 100 100 -2 -1 10000 10 10 10 10 Primary production (mg C m d ) Chl a (µg l-1) soest Bacteria (ml-1) 2 Figure captions: [A] Bacterial-C vs. phyto-C for LTER study area compared to 20-30% in other aquatic ecosystems; [C] and [D] DOC Antarctic data: log10 (Bgase) = -3.01 + 1.066 log10 (LAPase), r = 0.311, compared to relationships from temperate regions (Bird and Kalff, and DON vs. chl a contents of water samples, as a point of comparison p < 0.001, n = 398; [F] Relation between log HNF abundance (ml-1) and nsf dashed line and Cole et al., solid line), note the greater than 10-fold the has a chl a content of 0.05-0.1 µg l-1 but log bacterial prey (ml-1). The line describes the "Maximum Attainable deficit of bacteria compared to ecosystems elsewhere; [B] Bacterial DOC/DON of 100 mM and 6-7 mM, respectively; [E] BGase vs. LAPase Biomass" based on resources, from the model of Gasol (1994). (+) university of hawai‘i -1 -1 production (BP) vs. primary production (PP), note the low BP/PP ratios enzyme activities (Vsat , log10 of rates in nmol l d at in situ temp.) for a From non-polar marine environments, (•) from LTER region. variety of oceanic ecosystems. The regression line is the model 2 fit for